Neos\Media\Domain\Repository\ThumbnailRepository::iterate PHP Method

    public function iterate(IterableResult $iterator, callable $callback = null)
    {
        $iteration = 0;
        foreach ($iterator as $object) {
            $object = current($object);
            (yield $object);
            if ($callback !== null) {
                call_user_func($callback, $iteration, $object);
            }
            $iteration++;
        }
    }

 /**
  * Render ungenerated thumbnails
  *
  * Loops over ungenerated thumbnails and renders them. Optional ``limit`` parameter to limit the amount of
  * thumbnails to be rendered to avoid memory exhaustion.
  *
  * @param integer $limit Limit the amount of thumbnails to be rendered to avoid memory exhaustion
  * @return void
  */
 public function renderThumbnailsCommand($limit = null)
 {
     $thumbnailCount = $this->thumbnailRepository->countUngenerated();
     $iterator = $this->thumbnailRepository->findUngeneratedIterator();
     $this->output->progressStart($limit !== null && $thumbnailCount > $limit ? $limit : $thumbnailCount);
     $iteration = 0;
     foreach ($this->thumbnailRepository->iterate($iterator) as $thumbnail) {
         if ($thumbnail->getResource() === null) {
             $this->thumbnailService->refreshThumbnail($thumbnail);
             $this->persistenceManager->persistAll();
         }
         $this->output->progressAdvance(1);
         $iteration++;
         if ($iteration === $limit) {
             break;
         }
     }
 }